(a) Field of the Invention
The present invention relates to a preform for a glass ferrule and a fabrication method thereof, and more particularly to a preform for a dual hole ferrule made of glass, a fabrication method of the preform, and a fabrication method of the dual hole glass ferrule using the preform.
(b) Description of the Related Art
An optical ferrule, as an optical component, is used for connecting the cut ends of optical fiber to each other or to several optical devices. Optical fiber is inserted into the hole that is formed in the optical ferrule, and light is guided along the optical fiber.
Optical ferrules are generally classified as ceramic ferrules and glass ferrules. Ceramic ferrules are fabricated individually, while glass ferrules are fabricated by the same method as that of an optical fiber, that is, by using their viscous and flexible properties when heated.
A glass ferrule is fabricated by heating a glass preform, drawing the preform to a desired diameter in a drawing machine, cutting the preform having the desired diameter to a desired length, and processing its two ends and desired portions. The hole in the glass ferrule must be formed in parallel with the central axis extending along the lengthwise direction of the ferrule. Therefore, the hole in the glass preform must also be formed rectilinearly and in parallel with the central axis extending along the length direction of the preform.
In the case of a single-hole ferrule, a single hole having a desired diameter is formed at a center axis of the cylinder-shaped glass preform, and then the preform is elongated by use of a drawing machine while controlling the diameters of the preform and the hole to predetermined values.
However, in the case of dual-hole ferrule, the distance between the two holes, as well as the diameter of the preform and the hole, must be controlled.
FIGS. 1 and 2 are respectively longitudinal and horizontal cross-sectional views of a conventional preform for fabricating a glass ferrule. As shown in these figures, two holes 2 are rectilinearly formed in parallel with the longitudinal central axis (X), while maintaining the same distance from the center In the horizontal cross-sectional circle of the conventional preform 1.
Drawing the preform at an appropriate temperature and at an appropriate speed by a draw tower results in a ferrule in which two holes are formed in parallel with the central axis extending along the lengthwise direction of the preform. The distance between the two holes formed in the ferrule can be estimated from the original distance between the two holes formed in the preform, so a ferrule having a desired distance between the two holes can be attained by controlling the original distance.
That is, in order to fabricate a ferrule having a lesser distance between the two holes, a new preform which is processed to have a decreased original distance between the two holes is used.
Therefore, if the distance between the two holes formed in a desired ferrule is different from a previous ferrule, the preform must be changed to a new one. The work to change the preform is complicated, however, and it results in economic and time losses.
Moreover, polishing the inner surface of the hole after fabricating the ferrule is generally undertaken to improve the illumination of the optical device using the ferrule. Due to the polishing work, the fabrication process of the ferrule becomes complicated and it takes a long time, and therefore fabrication costs become high.